Deforestation

Deforestation

Deforestation can be defined as the conversion of forested areas to something that is different. Net deforestation accounts for afforestation (the establishment of forests on land that has not been recently forested), reforestation (the reestablishment of forests on land that was recently forested), and the natural expansion of forests. While the calculation of net deforestation is comparatively easy on a small scale, it is difficult on a global scale, despite modern technology such as extensive satellite surveillance. There are several reasons for this difficulty.

First, there is no universally agreed-upon definition of forest. The first Global Biodiversity Outlook (2001) defines forests as “ecosystems in which trees are the predominant life forms” but it also notes that a more precise definition is “surprisingly elusive” (p. 91). The Food and Agricultural Organization of the United Nations (FAO) has a more liberal definition, classing forests as “ecosystems dominated by trees (defined as perennial woody plants taller than 5 meters at maturity), where the tree crown cover exceeds 10% and the area is larger than 0.5 hectares” (a half of a hectare is about 1.2 acres) (FAO 2001, p. 365). This definition thus embraces areas that some investigators think too lightly wooded to be considered a forest.

The FAO definition of forest also includes tree plantations established for the production of timber or pulp-wood (used for paper) while excluding orchards. Critics point out that the inclusion of biodiversity-poor plantations in the definition of forests understates the loss of qualities that many people associate with the word “forest.” These qualities are found in woodland areas that retain a significant “natural” element and provide habitat for varied species, including trees of different species and ages. More controversially, the FAO includes in its definition forests that are “temporarily unstocked,” such as areas that have been cleared and burned. Because the duration of clearance and the certainty of restocking are unclear, inclusion of such temporarily cleared land complicates estimates of the extent and trend of current deforestation.

Other problems arise in determining the extent and trend of global deforestation. The aggregate data on which the FAO relies is supplied by its member states (as is the case with all global data used by the UN). The survey and statistical resources in many poor countries are weak, and often declining. The greatest disagreement over the extent of deforestation concerns the biodiversity-rich tropical forests. Yet such areas are disproportionately concentrated in countries where statistical resources are weak. Remote sensing methods have been increasingly used to try to compensate for these deficiencies. However, data obtained by these methods are also imperfect, for reasons such as persistent cloud cover and the problem of ground-truthing on a global basis (comparing satellite data with data observed on the ground).

About 8, 000 years ago, forests are estimated to have covered about 15 billion acres, almost half of the earth’s land surface. Since then human populations and fire have had a significant impact on these forests. This impact is roughly proportional to the increase in human population and its environmental impact. In the near future there is a risk that these effects may be multiplied by climate change.

A review by the Millennium Ecosystem Assessment— the most authoritative assessment of the causes, composition, and consequences of global deforestation—concluded that the world’s global forest area has shrunk by over 40 percent in recent centuries. The area of global forest in 2000 is thought to include from 9.6 to 10.9 billion acres.

The pattern of current deforestation shows two trends. At higher latitudes the boreal and temperate forest areas have either stabilized or are now expanding in size (by about 7.4 million acres per annum, of which about 2.5 million acres are plantations). However, in tropical regions, forests continue to decline in both area and quality (by about 30 million acres per annum).

Compared to the decade 1980-1990, net deforestation slowed in the following decade, from minus 30 million acres to minus 20 million acres per year. According to the Global Biodiversity Outlook 2 (2006), this trend in reduction in forest clearance has continued since 2000, with a loss of about 18 million acres per year in the five years to 2005. This decrease is mostly the result of expansion in plantations (including almost 5 million acres per annum in tropical regions). Thus, despite this slowing, the rate of loss of natural (“primary”) forests in the last two decades is thought to have remained about the same. Many forests are also declining in quality. Forest fragmentation, most commonly by the incursion of roads and agricultural settlements, leaves forests vulnerable to further disturbance, including drying, fires, and the invasion of exotic species.

Tropical rainforest is the most extensive forest type in the world, constituting 26 percent of global forest area. Almost 60 percent of existing tropical forests are rain forest; the remainder are mostly sparse forests in dryland areas and degraded forests. In tropical forests, biodiversity, including of trees, is very high, with often more than 100 tree species per hectare. Tropical forests (both moist and dry) harbor from 50 percent to 90 percent of the earth’s terrestrial species.

Most tropical forests are mainly in South America (1.4 billion acres), Africa (670 million acres), and Asia (490 million acres). From 1980 to 1990 about 25 million acres of tropical forest was cleared, of which about 15 million acres were of moist forests. In the following decade, total tropical forest clearance is thought to have increased to about 37 million acres per annum (about 1.2 percent of the global tropical forest total). While some of this loss is compensated for by tropical forest plantations, plantations are much lower in biodiversity.

Deforestation has largely occurred because of the expansion of agricultural land. Increasing populations and increasing demand for products that can be grown on land that is currently forested land (such as palm oil, a source of biofuel) will drive ongoing tropical deforestation. Climate change may worsen this, though it may also allow the expansion of some high-latitude forests, even if warmer winters allow increased populations of insect pests.

While there is considerable discussion of sustainable forest management, this is not yet having a significant mitigative effect. Until population growth substantially abates, the loss of quantity and especially of quality of forests in the tropics is likely to continue. And, because of climate change, tropical deforestation could continue even after population peaks.

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deforestation

deforestation The extensive cutting down of forests for the purpose of extracting timber or fuel wood or to clear the land for mining or agriculture. Forests are often situated in upland areas and are important in trapping rainwater. Deforestation in these areas, particularly in India and Bangladesh, has resulted in the flooding of low-lying plains; it has also led to an increase in soil erosion and hence desert formation (see desertification), resulting in crop loss and economic problems for local communities. The felling and burning of trees releases large amounts of carbon dioxide, thereby increasing global carbon dioxide levels and contributing to the greenhouse effect. Rainforests, particularly those of South America, are rich in both fauna and flora; their removal leads to an overall decrease in biodiversity and the loss of plant species that have potentially beneficial pharmaceutical effects. Despite movements to reduce deforestation, economic pressures ensure that the process still continues.

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Deforestation

Plant Sciences
COPYRIGHT 2001 The Gale Group Inc.

Deforestation

Deforestation occurs when the trees in a forested area are cut or destroyed faster than they can replace themselves. When too many trees are cut or destroyed, a very important element is taken from nature, making it difficult for the forest ecosystem to maintain a healthy balance in its natural cycle. The imbalance of the natural forest cycle threatens the humans, plants, and animals that depend on the forest for food, shelter, and protection. The loss of trees also causes negative effects on the natural cycles that affect water, soil, atmosphere, and weather.

Why Does Deforestation Occur?

Deforestation can be a natural or manmade process. Natural deforestation is caused by changes in weather patterns during glacial periods, fires started by lightning, windstorms, floods, and volcanic eruptions. Forests often recover from natural deforestation.

Deforestation caused by humans often results in permanent deforestation. Even when humans were living as small bands of hunters and gatherers they were deforesting areas for hunting animals or to practice swidden agriculture , planting areas they had cleared and moving on after the soil was spent. Over time, population levels grew and areas of permanent agriculture were established, around which civilizations began to grow. These civilizations began intensely farming fields to meet the growing demand for food. As civilizations expanded, more land had to be cleared for fields and forests had to be cut to meet the demand for wood products. The stress on forested areas grew as pressure was exerted from both swidden and permanent agriculture. These stresses intensified in times of conflict as people were forced to use more marginal areas or to overcut forests to meet their needs.

The Industrial Revolution and the technology that came with it has allowed the world population to grow at an exponential rate and has helped bring about a different lifestyle, one based on consumerism and sustained economic growth. The end result is that the last remaining areas that still have extensive forest cover, especially tropical forests, are being cut to satisfy unsustainable human consumption patterns and economic growth models. At the turn of the twenty-first century, more than one-half of the forests that once covered the globe were gone, with much of the cutting occurring over the last decades of the twentieth century.

Effects of Deforestation

The effects of deforestation can be both local and global. In the local forest ecosystem, trees, water, soil, plants, and animals are all dependent on one another to keep healthy. When trees are cut this natural balance is upset and the important functions that trees perform such as holding the soil in place, protecting groundwater, and providing food and shelter for plants and animals cannot take place. Overcutting forests and the disruption of the forest ecosystem are causing erosion of soil, the drop in water tables , loss of biodiversity as plant and animal species become extinct, loss of soil fertility, and the silting up of many water bodies. When the process continues for a long period of time or over a large area there can be total environmental collapse. Parts of the world that are now desert, such as Syria, Iraq, and Lebanon, were once covered with healthy forests.

Globally the effects of deforestation are more difficult to see. Forests play an important part in the greater natural cycles that make and affect the weather and that clean the air in our atmosphere. They keep the hydrological cycle healthy by putting water back into the atmosphere through transpiration , making clouds and rain. They also capture carbon dioxide produced by the burning of fossil fuels from the atmosphere, replacing it with oxygen and thus reducing the risk of global warming. If too many forests are cut these important functions cannot be carried out. The result could be less rain, higher temperatures, and more severe weather patterns in many regions of the world.

Local and global effects of deforestation are beginning to have devastating consequences. Some areas in West Africa, for example, are already feeling the effects of lost precipitation , higher temperatures, and increased desertification . Other areas, like Venezuela, have experienced devastating floods due to treeless slopes being unable to catch the rain from heavy storms, sending it rushing into valleys. All of these problems impact the environment, but they also take a heavy toll on humans.

Alternative Strategies to Deforestation

There are several things that can be done to decrease deforestation and to offset its negative effects. Many communities are trying to reduce the
burden placed on forests by instituting recycling programs and by using alternative materials like plastics in place of wood. In business, companies have begun to use wood products that come only from certified renewable forests that are carefully managed to ensure that they are cut in a sustainable way. Alternative methods of agriculture, such as agroforestry and permaculture , promote the use of trees and the diversification of crops to reduce the stress placed on forests by large-scale agriculture. Protecting forests by creating parks and reserves is another strategy to keep forest resources intact. For those areas that are already devastated, great efforts are being made to replant once-forested lands with native species.

Other efforts are aimed at changing our ideas about the value of forests. Economists are now trying to calculate the true value of the forest as an ecosystem and the benefits it gives as a whole, not only the value of cut logs. This reevaluation will help us make more informed choices about how we use forest land. All of these efforts have helped reduce the burden on the forests, but cutting continues unsustainably. Without the cooperation of all humans to create alternative strategies to deforestation, it will continue with terrible results for the health of our planet.

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deforestation

deforestation (disafforestation)1. The permanent clear-felling of an area of forest or woodland. On steep slopes this can lead to severe soil erosion, especially where heavy seasonal rains or the melting of snow at higher levels cause sudden heavy flows of water. In the humid tropics it may also lead to a release of carbon dioxide from the soil (owing partly to the loss of gases as soil structure deteriorates and partly to the decomposition of organic material, including tree roots).

2. A legal process whereby an area of forest land ceases to be regarded as forest under the terms of forest law.

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deforestation

deforestation(disafforestation)1. The permanent clear-felling of an area of forest or woodland. On steep slopes this can lead to severe soil erosion, especially where heavy seasonal rains or the melting of snow at higher levels cause sudden heavy flows of water. In the humid tropics it may also lead to a release of carbon dioxide from the soil (due partly to the loss of gases as soil structure deteriorates and partly to the decomposition of organic material, including tree roots).

2. A legal process whereby an area of forest land ceases to be regarded as forest under the terms of forest law.

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deforestation

deforestation Clearing away of forests and their ecosystems, usually on a large scale, by humans. It may be done to create open areas for farming or building, or for timber. There is an immediate danger that the vital topsoil will be eroded by wind (such as the dust bowl, USA) or, in hilly areas, by rain. Proposals to clear whole regions of the Amazonian rainforests, which play a key role in maintaining the oxygen balance of the Earth, could cause an environmental catastrophe.

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Deforestation

Environmental Encyclopedia
COPYRIGHT 2003 The Gale Group Inc.

Deforestation

Deforestation is the complete removal of a forest ecosystem and conversion of the land to another type of landscape. It differs from clear-cutting , which entails complete removal of all standing trees but leaves the soil in a condition to regrow a new forest if seeds are available. Humans destroy forests for many reasons. American Indians burned forests to convert them to grasslands that supported big game animals. Early settlers cut and burned forest to convert them to croplands. Between 1600 to 1909, European settlement decreased forest cover in the United States by 30%. Since that time, total forest acreage in the United States has actually increased. In Germany about two-thirds of the forest was lost through settlement. Food and Agriculture Organization (FAO) estimated that from 1980 to 1990, 0.9% of remaining tropical forests were deforested annually (65,251 mi2 [169,000 km2] per year), an area equivalent to the state of Washington. FAO defines forest as land with more than 10% tree cover, natural understory vegetation, nature animals, natural soils, and no agriculture. Analysis of deforestation is difficult because data is unreliable and the definitions for "forest" and "deforestation" keep changing; for example, clear-cuttings which reforest within five years have been considered deforested in some studies but not in others.

The major direct causes of topical deforestation are the expansion of shifting agriculture, livestock production, and fuelwood harvest in drier regions. Forest conversion to permanent cropland, infrastructure, urban areas, and commercial fisheries also occurs. Although not necessarily resulting in deforestation, timber harvest, grazing, and fires can severely degrade the forest. The environmental costs of deforestation can include species extinction , erosion , flooding , reduced land productivity, desertification , and climate change and increased atmospheric carbon dioxide . As more habitat is destroyed, more species are facing extinctions. Deforestation of watersheds causes erosion, flooding, and siltation . Upstream land loses fertile topsoil and downstream crops are flooded, hydroelectric reservoirs are filled with silt and fisheries are destroyed. In drier areas, deforestation contributes to desertification.

Deforestation can alter local and regional climates because evaporation of water from leaves makes up as much as two-thirds of the rain that falls in some forest. Without trees to hold back surface runoff and block wind, available moisture is quickly drained away and winds dry the soil, sometimes resulting in desert-like conditions. Another potential effect on climate is the large scale release into the atmosphere of carbon dioxide stored as organic carbon in forests and forest soils. In 1980, tropical deforestation released between 0.4 and 1.6 billion tons of carbon into the atmosphere, an amount equal to 10–40% of that from fossil fuels .

As a result of misguided deforestation in the moist and dry tropics, the rural poor are deprived of construction materials, fuel, food, and cash crops harvested from the forest. Species extinctions, siltation, and flooding expand these problems to national and international levels. Despite these human and environmental costs, wasteful deforestation continues. Current actions to halt and reverse deforestation focus on creating economic and social incentives to reduce wasteful land conversion by providing for wiser ways to satisfy human needs. Other efforts are the reforestation of deforested areas and the establishment and maintenance of biodiversity preserves.

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Deforestation

Deforestation refers to a longer-term conversion of forest to some other kind of ecosystem, such as agricultural or urbanized land. Sometimes, however, the term is used in reference to any situation in which forests are disturbed, for example by clear-cut harvesting, even if another forest subsequently regenerates on the site. Various human activities result in net losses of forest area and therefore contribute to deforestation. The most important causes of deforestation are the creation of new agricultural land and unsustainable harvesting of trees. In recent decades, deforestation has been proceeding most rapidly in underdeveloped countries of the tropics and subtropics.

The most important ecological consequences of deforestation are: the depletion of the economically important forest resource; losses of biodiversity through the clearing of tropical forests; and emissions of carbon dioxide with potential effects on global climate through an enhancement of Earth’s greenhouse effect. In some cases, indigenous cultures living in the original forest may be displaced by the destruction of their habitat.

Ever since the development of agriculture and settlements, humans have converted forest into agroeco-systems of various sort, or into urban land. There are numerous references in historical, religious, and anthropological literature to forests that became degraded and were then lost through overharvesting and conversion. For example, extensive forests existed in regions of the Middle East that are now almost entirely deforested. This can be evidenced by reference in the Bible to such places as the Forest of Hamath, the Wood of Ziph, and the Forest of Bethel, the modern locations of which are now desert. The cedars of Lebanon were renowned for their abundance, size, and quality for the construction of buildings and ships, but today they only survive in a few endangered groves of small trees. Much of the deforestation of the Middle East occurred thousands of years ago. However, even during the Crusades of the eleventh century through the thirteenth century, extensive pine forests stretched between Jerusalem (Israel) and Bethlehem (West Bank), and some parts of Lebanon had cedar-dominated forests into the nineteenth century. These are all now gone.

Similar patterns of deforestation have occurred in many regions of the world, including most of the Mediterranean area, much of Europe, south Asia, much of temperate North and South America, and, increasingly, many parts of the sub-tropical and tropical world.

From earliest times to the present, the global extent of deforestation has been about 12%. This

loss included a 19% loss of closed forest in temperate and boreal latitudes, and a 5% loss of tropical and subtropical forests.

However, in recent decades the dynamics of deforestation have changed greatly. The forest cover in wealthier countries of higher latitudes has been relatively stable. In fact, regions of western Europe, the United States, and Canada have experienced an increase in their forest cover as large areas of poorer-quality agricultural land have been abandoned and then regenerated to forest. Although these temperate regions support large forest industries, post-harvest regeneration generally results in new forests, so that ecological conversions to agriculture and other non-forested ecosystems do not generally occur.

In contrast, the rate of deforestation in tropical regions of Latin America, Africa, and Asia have increased alarmingly in recent decades. This deforestation is driven by the rapid growth in size of the human population of these regions, with the attendant needs to create more agricultural land to provide additional food, and to harvest forest biomass as fuel. In addition, increasing globalization of the trading economy has caused large areas of tropical forest to be converted to agriculture to grow crops for an export market in wealthier countries, often to the detriment of local people.

According to the Food and Agriculture Organization (FAO) of the United Nations (UN), as of 2005, the world’s forested areas stand at just under 9.9 billion acres (4.0 billion hectares), or about 30% of total land area of Earth. This figure is based on a new definition associated with the term forest; that is, areas including at least 10% of canopy cover but those areas excluding stands of trees that are included with primary agricultural production. In 2000, the amount of the world’s total forest area stood at 9.6 billion acres (3.9 billion hectares). From 1990 to 2000, the world’s forests experienced an average net annual loss of 23.2 million acres (9.4 million hectares) per year. From 1990 to 2005, deforestation has occurred most rapidly in the following regions of the world: West Africa, Central America and Mexico, and Southeast Asia. Among nations, the most rapid rates of deforestation are: Costa Rica, Ecuador, El Salvador, Haiti, Ivory Coast, Jamaica, Malawi, Nepal, Nicaragua, Nigeria, and Sri Lanka.

Now into the 2000s, deforestation mainly comes from conversion of forested lands to agricultural lands. This accounts for about 32 million acres (13 million hectares) per year. However, increased amounts of forest re-plantings, natural expansions, and landscape restorations have reduced the total rate of deforestation.

Past estimates of global deforestation have been criticized as unreliable. These surveys of forest changes, compiled by FAO, have been considered to be problematic because of inconsistencies in the collection methodology. Problems included potentially biased information (frequently from agencies within the country itself), inconsistent definitions of land use, and data gathering techniques that changed from survey to survey. These issues are being addressed through the use of remote sensing techniques and a more consistent definition of what is considered a forest. Satellite imaging of the forests is now being used to produce consistent and verifiable information on a global scale. Scientists and policy-makers involved with the issue of deforestation rely on dependable and accurate data. This reliable information permits them to monitor changes and accurately determine the extent of the forest.

Potentially, forests are a renewable natural resource that can be sustainably harvested to gain a number of economically important products, including lumber, pulp for the manufacture of paper, and fuel wood to produce energy. Forests also provide habitat for game species and, also, for the much greater diversity of animals that are not hunted for sport or food. In addition, forests sustain important ecological services related to clean air and water and the control of erosion.

Any loss of forest area detracts from these important benefits and represents the depletion of an important natural resource. Forest harvesting and management can be conducted in ways that encourage the regeneration of another forest after a period of recovery. However, this does not happen in the cases of agricultural conversion and some types of unsustainable forest harvesting. In such cases, the forest is mined (treated as a non-renewable-like resource) rather than treated as a renewable natural resource, and its area is diminished.

At the present time, most of Earth’s deforestation involves the loss of tropical forests, which are extremely rich in species. Many of the species known to occur in tropical forests have local (or endemic) distributions, so they are vulnerable to extinction if their habitat is lost. In addition, tropical forests are thought to contain millions of additional species of plants, animals, and microorganisms as yet undiscovered by scientists.

Tropical deforestation is mostly caused by various sorts of conversions, especially to subsistence agriculture, and to market agriculture for the production of export commodities. Unsustainable logging and fuel wood harvesting also cause tropical deforestation. Less important causes of tropical deforestation include hydroelectric developments that flood large reservoirs and the production of charcoal as an industrial fuel. Because these extensive conversions cause the extinction of innumerable species, tropical deforestation is the major cause of the global biodiversity crisis.

Mature forests contain large quantities of organic carbon, present in the living and dead biomass of plants, and in organic matter of the forest floor and soil. The quantity of carbon in mature forests is much larger than in younger, successional forests, or in any other type of ecosystem, including human agroecosystems. Therefore, whenever a mature forest is disturbed or cleared for any purpose, it is replaced by an ecosystem containing a much smaller quantity of carbon. The difference in carbon content of the ecosystem is balanced by an emission of carbon dioxide (CO2 ) to the atmosphere. This CO2 emission always occurs, but its rate can vary. The CO2 emission is relatively rapid, for example, if the biomass is burned, or much slower if resulting timber is used for many years and then disposed into an anaerobic landfill, where biological decomposition is very slow.

Prior to any substantial deforestation caused by human activities, Earth’s vegetation stored an estimated 990 billion tons (900 billion metric tons) of carbon, of which 90% occurred in forests. Mostly because of deforestation, only about 616 billion tons (560 billion metric tons) of carbon are presently stored in Earth’s vegetation, and that quantity is diminishing further with time. It has been estimated that between 1850 and 1980, CO2 emissions associated with deforestation were approximately equal to emissions associated with the combustion of fossil fuels. Although CO2 emissions from the use of fossil fuels has been predominant in recent decades, continuing

KEY TERMS

Conversion— A longer-term change in character of the ecosystem at some place, as when a natural forest is harvested and the land developed into an agroecosystem.

deforestation is an important source of releases of CO2 to the atmosphere.

The CO2 concentration in Earth’s atmosphere has increased from about 270 parts per million (ppm) prior to about 1850, to about 360 ppm in 1999, and it continues to increase. As of 2004, it stands at just over 377 ppm. Many atmospheric scientists hypothesize that these larger concentrations of atmospheric CO2 will cause an increasing intensity of an important process, known as the greenhouse effect, that interferes with the rate at which the Earth cools itself of absorbed solar radiation. If this theory proves to be correct, then a climatic warming could result, which would have enormous implications for agriculture, natural ecosystems, and human civilization.

Any solution to the problem of deforestation must first address the social and economic reasons for the activity. While population growth and social unrest have been cited as causes, the most important reasons for deforestation are economic. The average annual income of many people in those countries most heavily impacted by deforestation is at extremely low levels. These people are forced to survive by any means necessary including subsistence agriculture and utilization of wood for cooking and heating (about two-thirds of tropical people use wood fuels as their major source of energy, particularly poorer people). They often follow new logging roads to the only available property, forestland. The search for valuable hardwoods, such as mahogany and teak, is the other major source of forest clearing. Cattle ranching, plantations, and mining also provide considerable economic incentive for the destruction of forests. The social and economic value of these activities is much greater for the people involved than any perceived environmental value of the forests.

The Earth Summits of 1992 and 2002 attempted to address the linkage of social issues, economics, and the environment, though little agreement among nations was achieved. Some conservation organizations have shown that the economic wealth of one country can be traded for the environmental riches of another. A plan known as a debt-for-nature swap is one possible method for addressing both economic and environmental issues associated with deforestation. Many countries in which deforestation is rampant are relatively poor and are often in debt to more developed nations. Under the plan, the debt is bought (at a significant discount) in exchange for a pledge by the country to protect some portion of its valuable biologic resources, or to fund the activities of local conservation organizations within its borders. Agreements of this type have been emplaced in Bolivia, Madagascar, Zambia and other countries.

As of 2006, forestation experts state that slash-and-burn activities (clearing forests for agricultural use) within tropical forests, such as in Brazil, are the largest cause for deforestation in the world. Many countries try to reduce the rate of poverty and homelessness by using slash-and-burn activities to quickly improve the state of their citizens. It is estimated that over 200 million people around the world use slash-and-burn activities. However, such activities are extremely short-term in nature, causing quick erosion and exhaustion of the soils.

PERIODICALS

OTHER

National Aeronautic and Space Administration. “Better Monitoring of National and Global Deforestation Possible with Satellites.” May 30, 2001. <http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2001/200105304788.html> (accessed November 12, 2006).

Bill Freedman

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Deforestation

Environmental Science: In Context
COPYRIGHT 2009 Gale

Deforestation

Introduction

Deforestation is the clearing or cutting down of a forest for human activities such as agriculture. It has been going on for thousands of years, usually in response to population growth and the need for food and wood, which is important as a fuel and building material. In the modern era, deforestation is more extensive in developing countries.

Loss of forests has a number of environmental impacts. It can contribute to climate change, by reducing rainfall and altering the amount of sunlight reflected from Earth’s surface. Deforestation also increases the risk of forest fires by drying out the soil. Tree growth is important for biodiversity and for maintaining the quality of soil. Forests may also absorb considerable amounts of carbon dioxide, helping offset fossil fuel emissions. To reduce these impacts, a more sustainable approach to deforestation is desirable, using forestry practices that can preserve maximum tree cover.

Historical Background and Scientific Foundations

The reduction of areas of forest, known as deforestation, has been going on for at least 8,000 years, for a variety of reasons. The extent to which forest cover is decreasing varies from country to country, and it is widely accepted that Africa and Asia are the regions most affected, with deforestation being concentrated particularly in tropical areas. It is difficult to measure exactly how much deforestation has occurred. Direct methods involve going into the forest and measuring how much has disappeared. Remote sensing involves collecting data by satellite, without actually going into the forest. Remote sensing tends to give lower measures of the rate of deforestation than direct methods.

Remote sensing studies are useful in revealing a global picture of forest cover and patterns of deforestation. This reveals that in developed countries, forest cover is either stable, or even growing. In less developed countries, there is evidence of ongoing deforestation. Original forest still remains in Russia, Europe, and North America. Reforestation occurs either through deliberate re-planting of trees, or by succession, which is regrowth occurring naturally over time when a forest area has been disturbed. The new growth will not necessarily consist of the same species of tree that were originally present.

There are a number of different reasons for deforestation, related to either the trees themselves or the land they grow on. The need to use forests tends to be more pressing in developing countries. Wood has long been used as a source of fuel and as a building material. Globally, wood is a multi-billion dollar industry, accounting for about 2% of the world’s gross domestic product. North America and Scandinavia are important areas where deforestation occurs to harvest timber. Around half of wood harvested is used as fuel, the other half for building, paper manufacture, and other uses. In many African countries, wood is the main source of domestic fuel.

Clearing forests for agriculture is perhaps the most significant cause of deforestation. This is usually done by a slash-and-burn approach, where the farmer burns up the trees and vegetation to create a layer of nutrient ash. However, cleared forest is not nearly as fertile or productive as grasslands. It tends to be used by subsistence farmers in developing countries who cannot afford to buy imported foods or modern agricultural machinery or fertilizers that might allow them to produce a higher crop yield. Deforestation is also sometimes done in tropical regions to plant luxury crops like banana and pineapple which are in demand for export to richer nations.

WORDS TO KNOW

CLEAR-CUTTING: A forestry practice involving the harvesting of all trees of economic value at one time.

REMOTE SENSING: Acquiring data about an area such as forest without coming into contact with it.

SUCCESSION: Regrowth of forest following its disturbance by deforestation.

SUSTAINABLE: Capable of being sustained or continued for an indefinite period without exhausting necessary resources or otherwise self-destructing: often applied to human activities such as farming, energy generation, or the maintenance of a society as a whole.

Property rights can also lead to deforestation. In Brazil, in the 1980s and 1990s, the government granted property rights to areas of forest. Those who settled in the forest established these rights by clearing their area through burning. This led to substantial losses of tropical rain forest in Brazil. Other activities involving deforestation include mining, especially in Central and South America, and building dams, which often destroy forests through flooding. Additionally, these activities may destroy large areas of forest because they are supported by road building. This makes the forest more accessible to further activity, such as agriculture and human settlement.

Impacts and Issues

Deforestation has many impacts. Removal of trees reduces the biodiversity of the forest because so many species, from insects to birds, depend upon them. The species that remain may be affected by the fragmentation of their habitat. They may end up close to a road and thereby become more exposed to wind and rain. Loss of trees lets more sunlight into the forest, which dries the soil out and makes forest fires more likely. Fires emit many fine particles into the air that can upset precipitation patterns by allowing clouds to hold more moisture. Lack of rainfall promotes drought and makes further forest fires more likely. Removal of trees also causes soil erosion, which increases the risk of drought and flooding.

Deforestation also affects climate. Leaves transpire, or lose moisture, and solar energy is used in evaporating this. When a forest comes into leaf, there is often, therefore, a cooling effect. Loss of leaf cover allows more solar energy to warm Earth’s surface.

Forests may also act as a carbon sink. That is, they sequester carbon by absorbing it as carbon dioxide from the atmosphere through photosynthesis. The carbon is then stored, for varying periods of time, in the leaves, trunks, roots, and soil. One hectare of tropical forest can stored about 300-600 metric tons of carbon. Globally, forests can store billions of tons of carbon, which could significantly offset the carbon dioxide put into the air by the burning of fossil fuels. Deforestation may reduce the opportunity to use carbon sequestration to offset carbon emissions.

Deforestation, then, has many negative effects. However, forests do offer many obvious economic benefits in terms of their wood harvest and as a land source. Often the benefits of deforestation are more obvious than the negative effects and some governments promote deforestation by offering economic subsidies for farming there. Since it is highly unlikely that deforestation rates can be slowed down, the best approach might be to at least make it sustainable, so that timber taken is replaced by new growth of wood.

Forestry practices can be made sustainable. Clear-cutting is the traditional approach to harvesting timber where all of the trees with an economic value are taken. This is the cheapest method but selective harvesting, where only a certain number of trees are taken at any one time, has a less damaging impact. Another approach is shelter wood harvesting, where trees are partially cut for their wood, while others are left behind as shelter. Currently, there is no agreement over what the most sustainable approach is, as it likely depends upon local conditions. Consumers can play a part by demanding that products such as furniture be supplied only from sustainable forests.

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Deforestation

Encyclopedia of Population
COPYRIGHT 2003 The Gale Group Inc.

DEFORESTATION

Unlike the mere harvesting of trees for timber, deforestation changes a forest of growing trees into a different type of land cover. In France from 800 to 1300 c.e., the forests shrank by half, and in the United States from 1800 to 1920, the forests shrank by fully one-third. The replacement of forests, which ancient people might have seen as removing the lair of bandits and supernatural evil, in the twenty-first century seems a major transformation of the earth for the worse and hence an environmental threat.

Current Deforestation

During the 1990s the Food and Agriculture Organization (FAO) of the United Nations mounted a global survey to monitor changing forest areas. For the period from 1990 to 2000 FAO estimated that global deforestation was occurring at the average rate of 0.22 percent per year. Global forests shrank about 9 million hectares (ha) during the decade, an area roughly the size of Portugal or Hungary, or the state of Indiana. The global rates, however, cloak large regional differences, from 0.78 percent per year for deforestation in Africa, to its opposite, 0.08 percent per year afforestation in Europe. Among nations with more than one million ha of forest, the rates ranged widely–from deforestation at 3 percent or more per year in Niger, Ivory Coast, and Nicaragua to afforestation at 1 percent or more per year in seven nations as diverse as Belarus, China, Cuba, and Portugal.

Changes in land cover, including deforestation, are dynamic. The shrinkage of the earth's tropical forests from 1980 to 1990 was studied in a 1997 FAO survey of 3 billion ha of land (an area the size of Africa, or more than three times the land area of the United States) with several types of land cover. The forest with closed canopy in 1980 covered roughly half the surveyed area and is represented in Figure 1 as 100 percent. A decade later 93.3 percent of the 1980 forest was still closed; two percent of the 1980 forest had become open (i.e., open and fragmented forest plus long fallow); 1.8 percent had become shrub and short fallow; and 0.3 percent had been converted to plantations of trees. The largest conversion, 2.7 percent, was to other land cover, a category that includes permanent agriculture, cattle ranching, and water reservoirs, among others. Small conversions from open-canopied forest, and even smaller ones from the other classes of cover, to closed-canopy forest added a fraction of one percent to the 1990 closed forest. The small conversions to closed forest leave the impression that deforestation tends to be permanent.

Figure 2 describes forest change over almost the same decade (1982 to 1992) for a developed nation (the United States) that had earlier lost one-third of its forest. Fully 96.4 percent of non-federally-owned forest remained and conversions from other covers to forest slightly more than offset the lost 3.6 percent, expanding forest cover a little during the decade. Figures 1 and 2 exemplify the dynamic nature of changing land use, regional differences, and, instead of only deforestation, the possibility of afforestation.

The complexity of land cover change and differences in the definition of what a forest is make for uncertain estimates of the rate of deforestation. For example, the 0.5 percent change of forest to federal ownership shown in Figure 2 does not necessarily entail deforestation. Nor does the change from closed to plantation forest seen in Figure 1. FAO is attempting to generate consistent estimates of change using a uniform definition of forest area and applying remote-sensing techniques. In the end, while there is no doubt that deforestation is proceeding

FIGURE 1

in the tropics and afforestation is occurring in developed nations, some arbitrariness in estimated rates is inevitable.

Causes

Harvesting trees for lumber and pulp, even clear cutting the forest and allowing it to grow anew, does not qualify as deforestation. In developed nations, exemplified by the United States, lumber and pulp products have a declining role in the economy, so the overall impact of harvesting is diminishing over time. Authentic changes from forest to other cover occur when all the forest is removed for its products or the land is put to other use. Continually removing fuel wood can denude the land. In southern Africa, fuel wood accounts for about three-quarters of all energy use, and about 95 percent of all wood products were consumed for fuel. In the three rapidly deforesting countries cited above, Niger, Ivory Coast, and Nicaragua, two-thirds or more of the energy in each country came from wood in 1995. In the four countries that were mentioned above as having afforestation–Belarus, China, Cuba, and Portugal–wood represented less than one-twentieth of the energy source. In the first three countries population was rising faster than 2.4 percent per year during the period, while in the latter four the rate rose at less than 1 percent per year.

In 1803 economist T. R. Malthus wrote, "When acre has been added to acre till all the fertile land is occupied, the yearly increase of food must depend upon the amelioration of the land already in possession. This is a stream which, from the nature of all soils, instead of increasing, must be gradually diminishing" (Malthus 1992, p.17). Since Malthus wrote, the shrinkage of forests has often been attributed to expansion of cropland to supply an inexorably multiplying population. As countries have developed, however, they modified the connection between population size and cropland. Wealth increases expenditure on food but not in proportion to rising income. Eating more animal products can increase the need for feed, but the rise in protein intake per person tapers off in wealthy nations. Increasing yields per ha lower the need for cropland. In many countries, the events of the twentieth century produced an outcome that Malthus could not have envisioned: More and richer people were able to eat better while cropland scarcely changed or even shrank. In the 1990s in developed nations, the per capita supply of calories and protein and the total cropland declined by a fraction of 1 percent per year; in the developing world, calorie consumption rose by 0.7 percent per year and protein consumption by 1.2 percent, while cropland rose only by 0.3 percent per year.

Worldwide during the 1990s, a period during which the population was increasing by 80 million per year, forests shrank by nearly 1 million ha per year. But over the same period, cropland shrank–by 100,000 ha per year. Maintaining the Malthusian view that an increasing population requires more cropland, causing deforestation, thus becomes difficult. The role of grazing in deforestation is less clear because of the blurred distinction between pasture and woodland. (For this reason FAO abandoned reporting pasture area, although it did report that cattle numbers fell 2 percent per year in developed countries and rose 1.3 percent in developing countries during the period from 1990 to 1999.)

Geographers Alexander Mather and Coby L. Needle reasonably concluded from these estimates: "Outright rejection of the notion that forest trends are related to population trends is no more justifiable than an unqualified assertion that population growth is the driver of deforestation" (p.10).

Why Deforestation Matters

Why do some people see deforestation as an evil? An immediate reason is that eliminating forests may lead to a timber shortage. Traveling through New York and New England two centuries ago, President Timothy Dwight of Yale University worried that the voracious demand for fuel would deforest that region; yet at the beginning of the twenty-first century those areas again grow wide forests. The fear of timber shortage, of course, may be well justified in nations that continue to depend on fuel wood and are suffering deforestation.

Environmental consequences are another reason for concern about deforestation. Denuding land decreases evaporation from foliage and encourages rapid runoff and erosion. The loss of forest habitat can lead to the extinction of certain species. And, through diminished absorption of carbon dioxide in forest biomass, deforestation adds perhaps 20 percent to the carbon dioxide released from other anthropogenic sources, contributing to possible global warming.

Finally, the esthetic and emotional effects of deforestation, even if unmeasurable, cannot be ignored. Supported by myth, art, and literature, a veneration for forests persists.

Transition

An era of rising population and deforestation that has evolved into an era of afforestation in some nations despite rising population has been labeled the forest transition by Mather and Needle. If deforestation is feared and since the global population is certain to grow in the first part of the twenty-first century, this transition must continue to be the goal.

Planting trees directly expands forests. By the end of the twentieth century, forest plantations comprised 5 percent of global forest cover and were expanding at 2.4 percent per year. Plantations, which can sometimes produce timber faster than natural forests, can spare natural ones from harvest. Maintaining existing cropland in usable condition and raising crop yields spare forests from agricultural encroachment. Developing other types of fuel lessens the need to cut forests for fuel wood. These processes are contributing to the forest transition that is evident in an increasing number of countries in the first years of the twenty-first century.

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Deforestation

The Gale Encyclopedia of Science
COPYRIGHT 2008 The Gale Group, Inc.

Deforestation

Deforestation refers to a longer-term conversion of forest to some other kind of ecosystem , such as agricultural or urbanized land. Sometimes, however, the term is used in reference to any situation in which forests are disturbed, for example by clear-cut harvesting, even if another forest subsequently regenerates on the site. Various human activities result in net losses of forest area and therefore contribute to deforestation. The most important causes of deforestation are the creation of new agricultural land and unsustainable harvesting of trees. In recent decades, deforestation has been proceeding most rapidly in underdeveloped countries of the tropics and subtropics.

The most important ecological consequences of deforestation are: the depletion of the economically important forest resource; losses of biodiversity through the clearing of tropical forests; and emissions of carbon dioxide with potential effects on global climate through an enhancement of Earth's greenhouse effect . In some cases, indigenous cultures living in the original forest may be displaced by the destruction of their habitat .

Historical deforestation

Ever since the development of agriculture and settlements, humans have converted forest into agroecosystems of various sort, or into urban land. There are numerous references in historical, religious, and anthropological literature to forests that became degraded and were then lost through overharvesting and conversion. For example, extensive forests existed in regions of the Middle East that are now almost entirely deforested. This can be evidenced by reference in the Bible to such places as the Forest of Hamath, the Wood of Ziph, and the Forest of Bethel, the modern locations of which are now desert . The cedars of Lebanon were renowned for their abundance, size, and quality for the construction of buildings and ships, but today they only survive in a few endangered groves of small trees. Much of the deforestation of the Middle East occurred thousands of years ago. However, even during the Crusades of the eleventh century through the thirteenth century, extensive pine forests stretched between Jerusalem and Bethlehem, and some parts of Lebanon had cedar-dominated forests into the nineteenth century. These are all now gone.

Similar patterns of deforestation have occurred in many regions of the world, including most of the Mediterranean area, much of Europe , south Asia , much of temperate North and South America , and, increasingly, many parts of the sub-tropical and tropical world.

Deforestation today

From earliest times to the present, the global extent of deforestation has been about 12%. This loss included a 19% loss of closed forest in temperate and boreal latitudes, and a 5% loss of tropical and subtropical forests.

However, in recent decades the dynamics of deforestation have changed greatly. The forest cover in wealthier countries of higher latitudes has been relatively stable. In fact, regions of western Europe, the United States, and Canada have experienced an increase in their forest cover as large areas of poorer-quality agricultural land have been abandoned and then regenerated to forest. Although these temperate regions support large forest industries, post-harvest regeneration generally results in new forests, so that ecological conversions to agriculture and other non-forested ecosystems do not generally occur.

In contrast, the rate of deforestation in tropical regions of Latin America, Africa , and Asia have increased alarmingly in recent decades. This deforestation is driven by the rapid growth in size of the human population of these regions, with the attendant needs to create more agricultural land to provide additional food, and to harvest forest biomass as fuel. In addition, increasing globalization of the trading economy has caused large areas of tropical forest to be converted to agriculture to grow crops for an export market in wealthier countries, often to the detriment of local people.

In 1990, the global area of forest was 4.23 billion acres (1.71 billion ha), equivalent to 91% of the forest
area existing in 1980. This represents an annual rate of change of about -0.9% per year, which if projected into the future would result in the loss of another one-half of Earth's remaining forest in only 78 years. During this period of time deforestation (indicated as percent loss per year) has been most rapid in tropical regions, especially West Africa (2.1%), Central America and Mexico (1.8%), and Southeast Asia (1.6%). Among nations, the most rapid rates of deforestation are: Côte d'Ivoire (5.2%/year), Nepal (4.0%), Haiti (3.7%), Costa Rica (3.6%), Sri Lanka (3.5%), Malawi (3.5%), El Salvador (3.2%), Jamaica (3.0%), Nicaragua (2.7%), Nigeria (2.7%), and Ecuador (2.3%).

These are extremely rapid rates of national deforestation. A rate of forest loss of 2% per year translates into a loss of one-half of the woodland area in only 35 years, while at 3%/year the half-life is 23 years, and at 4%/year it is 18 years.

Past estimates of global deforestation have been criticized as unreliable. These surveys of forest changes, compiled by the United NationsFood and Agriculture Organization (FAO), have been considered to be problematic because of inconsistencies in the collection methodology. Problems included potentially biased information (frequently from agencies within the country itself), inconsistent definitions of land use , and data gathering techniques that changed from survey to survey. These issues are being addressed through the use of remote sensing techniques. Satellite imaging of the forests is now being used to produce consistent and verifiable information on a global scale. Scientists and policy-makers involved with the issue of deforestation rely on dependable and accurate data. This reliable information permits them to monitor changes and accurately determine the extent of the forest.

Loss of a renewable resource

Potentially, forests are a renewable natural resource that can be sustainably harvested to gain a number of economically important products, including lumber, pulp for the manufacture of paper , and fuelwood to produce energy . Forests also provide habitat for game species and also for the much greater diversity of animals that are not hunted for sport or food. In addition, forests sustain important ecological services related to clean air and water and the control of erosion .

Any loss of forest area detracts from these important benefits and represents the depletion of an important natural resource. Forest harvesting and management can be conducted in ways that encourage the regeneration of another forest after a period of recovery. However, this does not happen in the cases of agricultural conversion and some types of unsustainable forest harvesting. In such cases, the forest is "mined" rather than treated as a renewable natural resource, and its area is diminished.

Deforestation and biodiversity

At the present time, most of Earth's deforestation involves the loss of tropical forests, which are extremely rich in species. Many of the species known to occur in tropical forests have local (or endemic ) distributions, so they are vulnerable to extinction if their habitat is lost. In addition, tropical forests are thought to contain millions of additional species of plants, animals, and microorganisms as yet undiscovered by scientists.

Tropical deforestation is mostly caused by various sorts of conversions, especially to subsistence agriculture, and to market agriculture for the production of export commodities. Tropical deforestation is also caused by unsustainable logging and fuelwood harvesting. Less important causes of tropical deforestation include hydroelectric developments that flood large reservoirs and the production of charcoal as an industrial fuel. Because these extensive conversions cause the extinction of innumerable species, tropical deforestation is the major cause of the global biodiversity crisis.

Mature forests contain large quantities of organic carbon , present in the living and dead biomass of plants, and in organic matter of the forest floor and soil . The quantity of carbon in mature forests is much larger than in younger, successional forests, or in any other type of ecosystem, including human agroecosystems. Therefore, whenever a mature forest is disturbed or cleared for any purpose, it is replaced by an ecosystem containing a much smaller quantity of carbon. The difference in carbon content of the ecosystem is balanced by an emission of carbon dioxide (CO2) to the atmosphere. This CO2 emission always occurs, but its rate can vary. The CO2 emission is relatively rapid, for example, if the biomass is burned, or much slower if resulting timber is used for many years and then disposed into an anaerobic landfill , where biological decomposition is very slow.

Prior to any substantial deforestation caused by human activities, Earth's vegetation stored an estimated 990 billion tons (900 billion metric tons) of carbon, of which 90% occurred in forests. Mostly because of deforestation, only about 616 billion tons (560 billion metric tons) of carbon are presently stored in Earth's vegetation, and that quantity is diminishing further with time. It has been estimated that between 1850 and 1980, CO2 emissions associated with deforestation were approximately equal to emissions associated with the combustion of fossil fuels . Although CO2 emissions from the use of fossil fuels has been predominant in recent decades, continuing deforestation is an important source of releases of CO2 to the atmosphere.

The CO2concentration in Earth's atmosphere has increased from about 270 ppm prior to about 1850, to about 360 ppm in 1999, and it continues to increase. Many atmospheric scientists hypothesize that these larger concentrations of atmospheric CO2 will cause an increasing intensity of an important process, known as the greenhouse effect, that interferes with the rate at which Earth cools itself of absorbed solar radiation . If this theory proves to be correct, then a climatic warming could result, which would have enormous implications for agriculture, natural ecosystems, and human civilization.

Causes of deforestation

Any solution to the problem of deforestation must first address the social and economic reasons for the activity. While population growth and social unrest have been cited as causes, the most important reasons for deforestation are economic. The average annual income of many people in those countries most heavily impacted by deforestation is at extremely low levels. These people are forced to survive by any means necessary including subsistence agriculture and utilization of wood for cooking and heating (about two thirds of tropical people use wood fuels as their major source of energy, particularly poorer people). They often follow new logging roads to the only available property, forest land. The search for valuable hardwoods, such as mahogany and teak, is the other major source of forest clearing. Cattle ranching, plantations, and mining also provide considerable economic incentive for the destruction of forests. The social and economic value of these activities is much greater for the people involved than any perceived environmental value of the forests.

The Earth Summits of 1992 and 2002 attempted to address the linkage of social issues, economics, and the environment, though little agreement among nations was achieved. Some conservation organizations have shown that the economic wealth of one country can be traded for the environmental riches of another. A plan known as a "debt-for-nature" swap is one possible method for addressing both economic and environmental issues associated with deforestation. Many countries in which deforestation is rampant are relatively poor and are often in debt to more developed nations. Under the plan, the debt is bought (at a significant discount) in exchange for a pledge by the country to protect some portion of its valuable biologic resources, or to fund the activities of local conservation organizations within its borders. Agreements of this type have been emplaced in Bolivia, Madagascar, Zambia and other countries.

periodicals

other

National Aeronautic and Space Administration. "Better Monitoring of National and Global Deforestation Possible with Satellites." May 30, 2001 [cited January 31, 2003]. <http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2001/200105304788.html>.

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